The removal of sour gas or acid gas components such as hydrogen sulfide (H2S), carbon dioxide (CO2), carbonyl sulfide (COS), carbon disulfide (CS2) and mercaptans (RSH) from gas and liquid hydrocarbon streams is a process requirement in many parts of the hydrocarbon processing industry. Increasingly stringent environmental restrictions coupled with the need to process natural gas and crude oil with significant levels of sulfur requires sulfur recovery processes that can achieve high levels of conversion of hydrogen sulfide to elemental sulfur. The most common conversion method used is the Claus process. Approximately 90 to 95 percent (%) of recovered sulfur is produced by the Claus process.
The Claus process or Claus unit includes a thermal stage and a catalytic stage. The thermal stage can include a furnace, where hydrogen sulfide is reacted with oxygen to form sulfur dioxide (SO2) at high temperatures, such as temperatures greater than 800 degrees Celsius (deg C.). Hydrogen sulfide and sulfur dioxide can react in the thermal stage to form elemental sulfur and steam. The process gases from the thermal stage can be cooled and the elemental sulfur can be separated from the other gases. The separated process gases can be routed to the catalytic stage. In the catalytic stage, catalytic reactions occur at lower temperatures (as compared to the thermal stage) in two to three catalytic reactors, such that further elemental sulfur recovery is achieved. The Claus process typically recovers 95% to 97% of the hydrogen sulfide in the feed stream.
The Claus process is less efficient when the feed stream contains hydrogen sulfide concentrations less than 40% and can require oxygen enriched air or additional thermal and catalytic stages to reach higher sulfur recovery. Additionally, low hydrogen sulfide concentrations can require reactors with larger volumes to handle the oxygen concentration in the air.
A treatment unit can be placed upstream of the Claus unit to first recover hydrogen sulfide from a sour gas. The tail gas from the catalytic stage can be treated to increase sulfur recovery. Claus reaction thermodynamics allows only 70% of the sulfur to be recovered in the thermal stage and catalytic stages and subsequently tail gas treatment stages are required to reach target sulfur recovery. Selection of an appropriate and cost effective tail gas treatment process to follow existing Claus plants is a challenge facing refiners and natural gas plant owners around the world.